ZX-News #10 22 октября 1996

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Programmers - Some mysteries command input and output.

              Programmers



           Kostya Shelonin, 1996



       On some "secret" Command

               INPUT / OUTPUT

       we all loved CPU Z80.


  Do not worry, it will not that
A register is the high byte address
port teams, ispolzyyuschih immediate operand, and ... execution 
time commands IN / OUT. Many people are familiar skazhyt:

"What tyt mystery - he took, and looked at
reference ". But the thing is just a guide ...


  Some time ago, it took me
write protsedypy, which used to synchronize the port # FF 
(zakonchennyyu Test programmy, soderzhaschyyu ety protsedypy,

dymayu, you've nibyd yvidite and betaversiyu - tomorrow, if 
zainteresyetes). So, it would have been nice if not one little 
trouble - not converge the actual and estimated run time below 
this fragment. This made me prizadymatsya ...


 int IN A, (# FF)

         INC A

         INC BC

         JP NZ, int


  Estimated time - 31 bar

  Real-time performance - 32 cycles


  I looked in the directory data on komandy IN A, (n), takes 11 
clock cycles, and command IN A, (C) in 12 cycles, and decided

instead of 11 cycles prikinyt 12 ... AND
estimated time to come together with the real!


  This result is a bit puzzling, since
it's not a typo - in drygih references
also worth 11 clock cycles!


  In connection with this "mystery", I
conducted a series of experiments on zamery runtime commands IN 
and OUT, and here is a reward for the experiments: 


  n - 8-bit port address

  r - register, 8 bits


 team handbook really

IN A, (n) 11 cycles 12 cycles

IN r, (C) 12 cycles 12 cycles

OUT (n), A 11 clock cycles 12 cycles

OUT (C), r 12 cycles 12 cycles



    Drygie I / O commands are not checked!

P.S. If you have any questions,
can contact me by phone:


          (812) 151-44-43, Kostya


   Or soap on oridzhin (2:5030 / 41.30).

 With yvazheniem, K-Hacker from Omega group.


        __________________________